Senior Software Engineer, Backend

Summary

Join Flex, a NYC-based FinTech company revolutionizing rent payments, as a Senior Backend Engineer. You will play a key role in designing, building, and scaling backend services and APIs across four engineering teams: Consumer, Partner Integrations, Core Platform, and Risk. You will own the end-to-end lifecycle of your services, collaborate with cross-functional teams, and mentor junior engineers. Flex offers a competitive salary and benefits package. The company is growing rapidly and building an inclusive culture. This is an opportunity to make a significant impact on a mission-driven company.

Requirements

• Strong computer science fundamentals with a proven track record of building scalable backend systems
• 5–6+ years of professional software engineering experience with a focus on backend development
• 4+ years of hands-on Java experience , with deep knowledge of the Java ecosystem
• Proficient in Java frameworks and tools used at Flex: Spring (core/web/boot) , Gradle , JUnit , JVM tuning and performance optimization
• Experience operating services in distributed, service-oriented architectures at scale
• Familiarity with REST API design, mobile API best practices, and message-driven architectures
• Skilled at building robust, fault-tolerant systems and integrating with multiple external dependencies
• Hands-on experience with AWS (EKS, Aurora RDS, Elasticache, DynamoDB), containerization (Docker/Kubernetes), and Infrastructure as Code (CDK/Terraform)
• Skilled in observability and monitoring tools (e.g., DataDog ) to ensure high availability
• Ability to write high-quality code that is testable, maintainable, scalable, and secure, using industry best practices throughout the SDLC (unit testing, build automation, CI/CD)
• Excellent communicator, comfortable working with distributed teams and cross-functional stakeholders
• Proven ability to mentor junior engineers and raise the technical bar through best practices

Responsibilities

• Design, develop, test, and scale backend services and APIs that power Flex’s consumer products, partner integrations, risk management systems, and core platform services
• Build and operate robust, fault-tolerant distributed systems with multiple external dependencies
• Implement service APIs for web and mobile apps, simplifying complex rent payment processing
• Work closely with Product, Design, Infrastructure, Sales, Partner, and Customer Success to deliver features and integrations that delight customers and partners
• Translate feature requirements into technical specifications and lead the architecture and implementation of scalable solutions
• Drive the full lifecycle of services and APIs you build, including deployment, monitoring, and optimization for high availability and performance
• Contribute to evolving Flex’s service-oriented architecture, REST APIs, message queues, and scalable systems design
• Develop risk management systems such as rules engines, ML-powered fraud detection, and high-scale event ingestion pipelines
• Mentor junior engineers and help elevate the team’s engineering practices through code reviews, architecture discussions, and technical leadership
• Ensure services are observable and reliable using monitoring tools and industry best practices
• Collaborate on CI/CD improvements and automation to increase code quality and delivery velocity

Preferred Qualifications

• Experience designing and maintaining data pipelines and working with big data platforms (bonus: Snowflake)
• Risk Platform candidates: Experience in risk engineering, rules engine architecture, and implementing risk/fraud/credit policies in production systems is highly valued

Benefits

• 100% company-paid medical, dental, and vision
• 401(k) + company equity
• Unlimited paid time off + 13 company paid holidays
• Parental leave
• Flex Cares Program: Non-profit company match + pet adoption coverage
• Free Flex subscription
• Competitive Pay
• Company Equity
• Unlimited PTO